Telephone cables strung between spaced cable supports, typically telephone poles, are a familiar sight throughout the country, particularly in rural areas. A telephone cable normally consists of a plurality of twisted pair wires enclosed in a protective outer jacket. The telephone cables often have an outside diameter in excess of 21/2 inches (6.4 cm) and can weigh more than 6 pounds per lineal foot (8.9 kg/m). Therefore, it is a common practice to provide a cable support strand between the spaced-apart poles to support the weight of the telephone cable and reduce the strain on the electrical cable. A typical support strand can be a 3/8 inch to 1/2 inch diameter (1-1.3 cm) chromium-steel multi-wire strand. The telephone cable is supported by and hangs below the support strand, being attached thereto by lashing wire or other, similar means. For example, when lashing the telephone cable to the support strand, a chromium-steel wire having a diameter on the order of 0.045 inch (1 mm) is wrapped around the support strand and the telephone cable in a spiral-like manner between the supporting poles. Thus, the telephone cable and the support strand act as one system with the support strand carrying the entire weight of that system.
When a telephone cable and a support strand are mounted in the manner described above, there is generally in excess of 100 feet (30.5 m) of cable between supporting poles. The large diameter of the telephone cable combined with this length between poles presents a significant surface area to wind-generated high air flow velocities blowing on the cable. As the wind vector becomes more perpendicular to the longitudinal axis of the cable, there is a strong tendency for the cable to initiate a looping, harmonic oscillation about the longitudinal axis of the cable. This tendency increases with wind speed, leading to metal fatigue and failure--disrupting transmission service over the cable. In order to prevent breakage, telephone and power companies have utilized a system of aluminum vibration dampers that are attached to the cable system to inhibit the vibrations cause by wind.
A typical wind damper comprises a sheet of aluminum or other similar material formed into an aerodynamic shape and suspended below the cable system. One such damper, known in the trade as a "bat wing", is shown in U.S. Pat. No. Des. 207,317 issued on Apr. 4, 1967, to Curtis M. Wright. The shape of the damper causes it to "catch" the wind in much the same manner as a sail, dramatically increasing the air resistance of the cable. The added resistance translates to a sufficient energy loss to a potential free harmonic oscillation as to prevent such motion from occurring. In addition, the resistance increases with increasing wind speed, matching the increased tendency to generate the oscillation. More than one wind damper can be used in a section of the cable system if the distance between adjacent poles is great or the cable system is in a high wind area.
In order to be effective, the wind damper must be allowed to pivot freely about the lower half of the cable system. In the current state of the art, the wind damper is supported by a pair of screw clamps, identical to those frequently used as automotive hose clamps, (i.e., periodic slots are formed in a metal band with a screw that is engageable with the slots located at a non-slotted end to tighten the band around the hose or, in this case, the supported cable system). Unfortunately, the screw clamps are not particularly suited for the stresses applied by the cable/damper system, and a high failure rate has been encountered. One reason for the failures resides in the structure of the screw clamp itself. The slots in the metal band weaken the band, and the clamp was really not designed to withstand the variable peak loading characteristics inherent in the wind damper system. Over time, metal fatigue occurs until the band can no longer respond to loads caused by shifts in the wind and breaks.
A second failure mode results from the requirement that the wind damper support must allow the wind damper to freely pivot. This freedom is accomplished by hanging the wind damper from a screw clamp that has been loosely mounted about the suspended cable. The tendency for the wind dampers to longitudinally move along the wire is resisted by the placement of lashing wire clamps (known as "bug nuts") adjacent the clamps on the supported cable. These clamps always loosen, and under certain wind conditions, the hose clamp can "jump" and can move past the lashing wire clamp and allow the wind damper to move along the wire.
The screw clamps are expensive and telephone companies have found that there is a significant cost in labor and materials to install and maintain the wind dampers in proper operational condition. Therefore, a need exists for an improved system for mounting the wind dampers to a telephone cable system.